The compressor control system is illustrated in the context of the inventions disclosed in the aforestated U.S. patent applications. The present invention combines, for an overall treatment of a compressor system, the operation from loading to unloading, as well as for a long term under a continuous, or discontinuous, load demand. In this context, the present invention copes with the situation when a compressor is used working into a small capacity system, what would have the unfavorable consequence, when loading, of calling for an excessive demand for airflow in order to meet the assigned setpoint pressure of the compressor system of larger capacity. The excessively large flow toward the small tank will result in a backlash into the compressor, and a surge. As seen from the master-controller, the operation involves a setpoint assigned to the system. When a large compressor is used with a tank which is of smaller capacity, the reaction to the air pressure building too quickly during loading will cause the system to overshoot the setpoint assigned by the operator, and a surge will occur due to such overpressure.
It is known from U.S. Pat. No. 4,080,110 to provide a variable capacity gas compressor, thereby to meet the requirements of the load by regulating the capacity of the compressor.
The present invention involves a constant airflow compressor of relatively large capacity in operation with a small capacity system. Adjusting the parameters of the control system to increase the rate of response to meet the overshoot will not do, because, under inlet valve modulation, the inlet valve will tend to respond to the overshoot by closing too quickly toward the minimum air flow position P2, thereby undershooting the limit valve position so that, again, a surge will occur.